A month is long enough for Oro to dribble the rift scar to a secret location, turn around, and team up with Leopard+Pangolin+other allies to kill Cannai.
Maybe this can be countered by letting Cannai choose to leak early, but maybe that can be countered by threatening the extinction of Dogs if Cannai does anything beyond what his oaths require.
We've seen Hazou can reverse-summon while he has a severe several times. One week is fine, and doesn't give Oro enough time to attack Cannai or otherwise defuse the deadman.
I appriciate the sentiment, but Cannai's the best choice, I don't think anyone else anyone has a summon in dog right now, and it lets Cannai check in on Hazou firsthand.
There are advantages to both Hazo-controlled and Blind-Hazou deadman systems, so we should simply do both methods in parallel.